The standard picture: a black hole has entropy proportional to the area of its event horizon. As it evaporates via Hawking radiation, the entropy flows out. The black hole is a container — it holds entropy, then releases it.
Unruh proposes the opposite. A black hole does not contain entropy. It creates it. The distinction is not semantic. A container's entropy decreases as entropy leaves; a creator's entropy is generated in the act of emission. The total entropy emitted over the black hole's lifetime is the same — proportional to the square of its mass — but the mechanism and interpretation differ fundamentally.
The argument proceeds via analogy with a linear amplifier. An amplifier has no inherent entropy. Feed it a signal (vacuum fluctuations, in the black hole case), and it produces an output (thermal radiation) that carries entropy the amplifier generated, not stored. The amplifier's operation creates correlations between input and output modes that, when the input is traced over, appear thermal. The entropy is in the tracing, not in the device.
The black hole's relationship to its own entropy parallels the amplifier's: the information in the infalling quantum state is not lost inside the black hole but is amplified and mixed with the outgoing radiation in a way that generates entropy. The black hole is not a vault from which entropy must somehow escape. It is a process — one that manufactures entropy rather than hoarding it.